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    <meta charset="UTF-8">
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    <title>Document</title>
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<body>
    <script>
    /* other-->boolean  Boolean();
    就这五种情况为false
    "",0,NaN,undefined,null-->false
     */
    var a = "hello";
    var b = 20;
    console.log(Boolean(a));
    console.log(Boolean(b));
    console.log(""==0);
    console.log(undefined == null);
    </script>
</body>
</html>